Add blog post for Rust 1.91.1

content/Rust-1.91.1.md

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+path = "2025/11/10/Rust-1.91.1"
+title = "Announcing Rust 1.91.1"
+authors = ["The Rust Release Team"]
+aliases = ["releases/1.91.1"]
+
+[extra]
+release = true
++++
+
+The Rust team has published a new point release of Rust, 1.91.1. Rust is a
+programming language that is empowering everyone to build reliable and
+efficient software.
+
+If you have a previous version of Rust installed via rustup, getting Rust
+1.91.1 is as easy as:
+
+```
+rustup update stable
+```
+
+If you don't have it already, you can [get `rustup`][rustup] from the
+appropriate page on our website.
+
+[rustup]: https://www.rust-lang.org/install.html
+
+## What's in 1.91.1
+
+Rust 1.91.1 includes fixes for two regressions introduced in the 1.91.0 release.
+
+### Linker and runtime errors on Wasm
+
+Most targets supported by Rust identify symbols by their name, but Wasm
+identifies them with a symbol name *and* a Wasm module name. The
+[`#[link(wasm_import_module)]`][wasm_import_module] attribute allows to
+customize the Wasm module name an `extern` block refers to:
+
+```rust
+#[link(wasm_import_module = "hello")]
+extern "C" {
+    pub fn world();
+}
+```
+
+Rust 1.91.0 introduced a regression in the attribute, which could cause linker
+failures during compilation (*"import module mismatch"* errors) or the wrong
+function being used at runtime (leading to undefined behavior, including crashes
+and silent data corruption). This happened when the same symbol name was
+imported from two different Wasm modules across multiple Rust crates.
+
+Rust 1.91.1 fixes the regression. More details are available in [issue #148347].
+
+[wasm_import_module]: https://doc.rust-lang.org/reference/items/external-blocks.html#r-items.extern.attributes.link.wasm_import_module
+[issue #148347]: https://github.com/rust-lang/rust/issues/148347
+
+### Cargo target directory locking broken on illumos
+
+Cargo relies on locking the `target/` directory during a build to prevent
+concurrent invocations of Cargo from interfering with each other. Not all
+filesystems support locking (most notably some networked ones): if the OS
+returns the `Unsupported` error when attempting to lock, Cargo assumes locking
+is not supported and proceeds without it.
+
+Cargo 1.91.0 switched from custom code interacting with the OS APIs to the
+[`File::lock`] standard library method (recently stabilized in Rust 1.89.0). Due
+to an oversight, that method always returned `Unsupported` on the illumos
+target, causing Cargo to never lock the build directory on illumos regardless of
+whether the filesystem supported it.
+
+Rust 1.91.1 fixes the oversight in the standard library by enabling the
+[`File::lock`] family of functions on illumos, indirectly fixing the Cargo
+regression.
+
+[`File::lock`]: https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.lock
+
+### Contributors to 1.91.1
+
+Many people came together to create Rust 1.91.1. We couldn't have done it
+without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.91.1/)